The present invention relates to printed circuit boards and particularly to a method of making a circuit board on the surface of which electronic components are mounted using solder reflow processing.
Various computing apparatuses (e.g., notebook computers) for which miniaturization is a continuing design objective typically utilize electronic components of a surface mounting type which are mounted on the apparatus circuit board(s) at the highest density possible in order to reduce the circuit board""s required real estate.
Solder reflow for soldering electronic components onto a printed circuit board is a known and widely used process. During reflow, the circuit board may be bent (e.g., upwardly) due to exposure to the heat generated during the reflow process, or it may be downwardly bent due to said heat and the weight of the electronic components mounted thereon. As a result, unacceptable gaps may form between the circuit board and the electronic components mounted thereon to the extent that electronic component and circuit board solder failures result. The board must then be scrapped or subjected to extensive rework, both relatively costly to the board manufacturer and component assembler.
A printed circuit board apparently designed to reduce bending of the circuit board during a reflow process is described in Japanese Unexamined Patent Publication No. Hei 5-226792. FIG. 1 of the present drawings is a view of this printed circuit board. Specifically, a printed circuit board 1 has perforations 2 formed within its surface, the perforations 2 defining a circuit board portion 3 on which electronic components are to be mounted. Surrounding board portion 3 is an edge portion 4. Multiple tiny openings (slits) 5 formed in surrounding portion 4 are substantially perpendicular to the direction (6) in which the printed circuit board is transported during the reflow process.
The circuit board of FIG. 1 is effective because during the reflow process, the tiny elongated openings 5 formed in surrounding portion 4 help to reduce the bending of the circuit board in the feeding direction (6). A conventional circuit board, not having such slits, is not as effective in reducing such board deflection in said direction.
It is believed that a method of making a printed circuit board that prevents solder failures between components and connection pads thereon in a new and unique manner in comparison to the approach described in the foregoing Japanese publication would represent a significant advancement in the art.
It is, therefore, a primary object of the present invention to enhance the printed circuit board art.
It is another object of the invention to provide a method of making a printed circuit board which can be effectively produced on a large scale without harm to solder connections between the board""s circuitry and the leads of components coupled thereto.
It is a more particular object of the invention to provide such a method which substantially prevents solder disconnections caused by board deflection during processing, especially during solder reflow.
In accordance with one aspect of the invention, there is provided a method of making a printed circuit board adapted for having electronic components mounted thereon involving a solder reflow process, the board comprising a circuit portion having an electrical circuit thereon, a circumferential portion substantially surrounding the circuit board, and at least one elongated opening formed within the surrounding circumferential portion substantially parallel to the predetermined direction the printed circuit board moves during the solder reflow process to substantially prevent electronic component solder failures that occur as a result of the deflection of the printed circuit board during the reflow process.